Conventionally, as a two-wire power transmission method for performing power transmission/reception and intercommunications using two power transmission wires, there is a high-frequency superimposition method for superimposing a high-frequency signal onto the transmission wires for power transmission. In the high-frequency superimposition method, a power receiving side device includes a high-frequency bandpass filter, thereby detecting only a high-frequency signal. Also, a method for superimposing a phase-modulated pulse signal onto DC two transmission wires for power transmission, and a method for causing one of DC two-wires to be interrupted or shorted out at regular intervals, thereby performing pulse-like transformation for direct power for power transmission, are also known.
On the other hand, in Japanese Patent Examined Publication No. S54-40304, a method for performing time-shared power transmission of power and a signal is disclosed. This method is a method for transmitting the power and the signal over a pair of transmission wires by performing time-shared power transmission of the power and the signal from a power transmitting side. The power is ten smoothed by a condenser, etc., so as to be a direct current, a logic circuit and a relay drive circuit, etc., are activated, and the power and the signal are demultiplexed by detecting their differences in width and height, etc., in a power receiving side. Compared to the above-described high-frequency superimposition method, or the like, this method can realize power transmission/reception and communications at low cost with a simple circuit. Also, as a method for performing time-shared power transmission of the power and the signal, a method enabling bi-directional communications capable of specifying which power receiving side device processes the signal, by assigning an address to a signal to be transmitted, or capable of identifying a transmitting side which has transmitted the signal is also known.
However, the above-described high-frequency superimposition method has to use a complicated circuit structure and high-cost circuit parts for modulation in order to improve signal leakage and noise immunity, thereby increasing costs. Also, the above-described method for performing superimposition for a phase-modulated pulse signal for power transmission has a limit in a transmission speed, and the method for causing one of DC two-wires to be interrupted or shorted out at regular intervals has a problem that there is always noise, whereby both methods do not allow many power receiving side devices to be connected from the aspect of transmission efficiencies. Furthermore, as for the above-described method for performing time-shared power transmission for the power and the signal, a signal from the power transmitting side cannot be distinguished from a signal from the power receiving side based on a voltage, etc., and the power receiving side has to receive all signals from the power transmitting side and all signals from another power receiving side, and determine whether or not these are effective data addressed thereto, thereby complicating a process and increasing a burden in the power receiving side. As a result, a cost of software, etc., performing a process at the power receiving side is increased.
Therefore, an object of the present invention is to provide a low-cost and transmission-efficient two-wire power transmitting/receiving communication apparatus and method, which reduce a processing burden of the power receiving side.